Regenerative system for the simultaneous removal of particulates and the oxides of sulfur and nitrogen from a gas stream

ABSTRACT

A process and system for simultaneously removing from a gaseous mixture, sulfur oxides by a solid sulfur oxide acceptor sorbent on a porous carrier, nitrogen oxides by ammonia gas and particulate matter by filtration and for the regeneration of loaded solid sulfur oxide acceptor sorbent. Finely-divided solid sulfur oxide acceptor sorbent is entrained in a gaseous mixture to deplete sulfur oxides from the gaseous mixture, the finely-divided solid sulfur oxide acceptor sorbent being dispersed on a porous carrier material having a particle size up to about 200 microns. In the process, the gaseous mixture is optionally prefiltered to remove particulate matter and thereafter finely-divided solid sulfur oxide acceptor sorbent is injected into the gaseous mixture to form an entrained bed. Ammonia gas is also injected into the exhaust gas stream. A filter separates spent solid sorbent and particulate matter from clean gas. A classifier is used to separate mixtures of spent sorbent from particulate matter. A regenerator receives spent sorbents for regeneration and regenerated finely-divided solid sorbent is passed from the regenerator to the entrained bed reactor. A preferred sorbent is copper oxide on porous alumina carrier.

This is a division of application Ser. No. 07/905,133 filed Jun. 23,1992, now U.S. Pat. No. 5,202,101, issued Apr. 13, 1993.

BACKGROUND OF THE INVENTION

This invention relates to a process and system for reducing theconcentration of pollutants contained in a gaseous mixture, and moreparticularly, to a process and system for the removal of particulatematter and the oxides of nitrogen and sulfur from a gaseous mixture, aswell as the regeneration and recycling of spent sorbent used to removethe oxides of sulfur from the gaseous mixture.

Particulate matter and the oxides of sulfur and nitrogen result from thecombustion or air oxidation of carbon-containing materials, such ascoal, fuel oil and the like, and are responsible for major amounts ofpollution in our environment. Currently, the commercially availableprocesses and systems for the removal of oxides of sulfur and nitrogenand particulate matter from combustion gases resulting from thecombustion or air oxidation of coal or fuel oil in power plants aregenerally very expensive to build and to operate. The removal of eachcontaminant requires a large scale system and produces large quantitiesof waste.

A large number of processes and systems have also been proposed in theliterature, including the processes and systems discussed in U.S. Pat.Nos. 3,501,897; 3,776,854; 3,816,597; 3,840,643; 3,966,879; 4,101,634;4,164;546; 4,170,627; 4,192,855; 4,193,972; 4,258,020; 4,609,537;4,692,318; 4,744,967 and 4,851,202, all of which are incorporated hereinby reference in their entirety. In the foregoing references, either SO₂is removed; or NO_(x) is removed; or SO₂ and NO_(x) as well asparticulate matter are removed from combustion gases, usually by usingsolid sulfur oxide acceptors and/or ammonia gas. In certain instances,it is also known to regenerate the spent or loaded sulfur oxide acceptorby various means as described in U.S. Pat. Nos. 3,501,897; 3,776,854;3,778,501; 3,846,536; 4,001,376; 4,101,634; 4,164,546; 4,192,855;4,609,537 and 4,692,318, all of which are incorporated by referenceherein in their entirety. In many of the references, the solid sulfuroxide acceptor is used in the form of a moving bed, a fluidized bed, afixed bed or in a "parallel passage" reactor, and both the removal ofsulfur oxides with solid sulfur oxide acceptor and the regeneration ofthe spent or loaded solid sulfur oxide acceptor are inefficient,inadequate and/or expensive.

In most instances in the prior art, copper, copper oxide or a mixturethereof is coated on alumina or impregnated in alumina to form solidsorbents for the removal of sulfur dioxide from gases. In U.S. Pat. No.3,966,879, sulfur oxides and particulate matter are removed from wastegases in the same processing zone under the reaction conditions requiredfor sulfur oxide acceptance in a moving bed which contacts the waste gasstream in cross-current fashion.

The reduction of the nitrogen oxides (NO_(x)), both NO and NO₂, to freenitrogen with ammonia in the presence of a copper oxide-containingcatalyst is described in U.S. Pat. No. 4,101,634 where it is alsoindicated that the conversion of nitrogen oxides with the simultaneousremoval of sulfur oxides by means of a copper-containing acceptor provesnot to exceed 70 percent.

In U.S. Pat. No. 4,101,634 sulfur oxides and nitrogen oxides are removedsimultaneously by use of a metal-containing acceptor with continuousaddition of ammonia or precursor thereof with some improvement inefficiency when the metal-containing acceptor is regenerated at regularintervals by a reducing gas passed counter-currently in the bed; theregeneration is terminated at the moment when at least some of theacceptor is still in the sulfate form; and the oxygen-containing gasstream to be purified is then re-contacted with the acceptor with thesimultaneous addition of ammonia or precursor.

In U.S. Pat. No. 4,164,546, nitrogen oxides are removed from a gaseousmixture containing nitrogen oxides and oxygen by addition of ammoniathereto and by contacting with a suitable catalyst for thenitrogen-ammonia reaction wherein best results are achieved when sulfurdioxide is also present in the gaseous mixture and wherein excess sulfurdioxide is separated prior to the nitrogen oxide conversion,simultaneously therewith or subsequent thereto. In U.S. Pat. No.4,164,546, fixed beds of the contact mass, such as copper oxide onalumina are preferred for effective removal of both sulfur dioxide andnitrogen oxide with regeneration by a reducing gas such as hydrogen,methane, ethane, propane and the like. Further, in U.S. Pat. No.4,164,546, it is indicated that the flue gas may contain small amountsof finely-divided suspended particulate matter such as fly ash.

In U.S. Pat. No. 4,193,972, sulfur dioxides are removed from a gasstream by the use of a metal-containing regenerable acceptor andnitrogen oxides contained in the gas stream are reduced to nitrogen gasin a parallel passage vapor-solids contactor which is conventional forprocessing gas streams containing particulate matter, such as fly ash,and wherein-the reduction of nitrogen oxides to nitrogen is catalyzed bycopper sulfate on alumina. In U.S. Pat. No. 4,193,972, the reduction ofnitrogen oxides to nitrogen may be carried out simultaneously with theacceptance of sulfur oxides on copper-containing acceptors, and thereaction may be preceded by the admixture of ammonia into the gas streambeing treated.

Although regenerative processes wherein spent or loaded solid acceptorused to absorb sulfur dioxide from gas streams is regenerated inprocesses and systems for the simultaneous removal of sulfur dioxide,NO_(x) and particulate matter from gas streams are well-known, theprocesses and systems remain disadvantageous because they areinefficient, require high capital investment when utilized in largescale systems and are expensive to operate in large plants, such aspower plants which utilize combustible coal or fuel oil. Even though acertain amount of waste has been eliminated by the foregoing prior artregenerative processes, none of the emerging processes and systemsdiscussed above have gained a wide industrial acceptance due to theirhigh cost and complexity.

SUMMARY OF THE INVENTION

In view of the fact that pollution of our environment with gaseousmixtures containing particulate matter and the oxides of sulfur andnitrogen remains a problem, it is desirable to improve the efficiency ofthe removal of particulate matter and the oxides of sulfur and nitrogenfrom gas streams and to reduce capital cost of and expense of operatinglarge scale systems dedicated to providing clean air. Accordingly, it isdesirable to provide a regenerative process and system for the efficientand simultaneous removal of particulate matter and the oxides of sulfurand nitrogen from gases containing these pollutants.

Generally, the present invention is defined by a system and process inwhich particulate matter, sulfur oxides and nitrogen oxides are removedsimultaneously by use of a metal-containing acceptor, with continuousaddition of ammonia, or precursor thereof, and the sulfur oxide acceptoris regenerated continuously or at regular intervals (intermittently) bya reducing gas or by thermal decomposition, without the disadvantages ofthe prior art. In one aspect, the process is characterized in that theregeneration of the loaded sulfur oxide acceptor is effected by passingreducing gas through a fluidized loaded sulfur oxide acceptor bed toform regenerated acceptor. The gas stream to be purified is thencontacted with the regenerated acceptor in an entrained bed with theaddition of ammonia or ammonia precursor.

In accordance with the present invention, a highly efficient process andsystem for the simultaneous removal of particulate matter and the oxidesof sulfur and nitrogen has been achieved by using a finely-divided solidacceptor for the oxides of sulfur on a suitable porous carrier, and bysimultaneously using ammonia gas or a precursor thereof for the oxide ofnitrogen, followed by filtration. The solid acceptor for sulfur oxideson a suitable carrier must be used in a reactor wherein an entrained bedof the solid acceptor for sulfur oxides is formed, that is, a reactorcapable of forming an entrained bed of the finely-divided solid sorbentfor the oxides of sulfur in a gas stream, such as a combustion exhaustgas-stream. When a finely-divided solid sorbent on a suitable porouscarrier is utilized, it is highly reactive and requires a very shortcontact time to absorb the oxides of sulfur and to reduce the oxides ofnitrogen in the presence of ammonia gas when used in the reactor capableof forming an entrained bed of the finely-divided sorbent in the gasstream. The process and system of the present invention is highlyefficient when the finely-divided solid acceptor for sulfur oxides isincorporated in and/or dispersed on a porous carrier material having aparticle size up to about 200 microns and in certain embodiments aparticle size of about 20 microns to about 200 microns. It is thecritical combination of using the finely-divided sorbent and the highlyporous carrier material which imparts high efficiency to the capacity ofthe sorbent to remove sulfur oxides from a gas stream when the sorbentis merely entrained in a stream of the gas to form an entrained bed.

In one aspect of the present invention, there is provided a process forsimultaneously removing from a gaseous mixture, oxides of sulfur bymeans of a solid sulfur oxide acceptor on a porous carrier, oxides ofnitrogen by means of ammonia gas and particulate matter by means offiltration, by (a) filtering the gaseous mixture to remove particulatematter when particulate matter in the gaseous mixture is coarser than orabout the same size as the solid sulfur oxide acceptor on a porouscarrier, thereby forming a prefiltered gaseous mixture; (b) forming anentrained bed of solid sulfur oxide acceptor in the gaseous mixture todeplete sulfur oxides in the gaseous mixture and thereby convert solidsulfur oxide acceptor to loaded or spent solid sulfur oxide acceptor,the solid sulfur oxide acceptor being dispersed on a porous carriermaterial wherein the porous carrier material has a particle size up toabout 200 microns when the gaseous mixture is prefiltered and a particlesize of about 20 to about 200 microns when prefiltering is omitted; (c)injecting ammonia gas or a precursor capable of forming ammonia gas intothe gaseous mixture prior to, during or after the formation of theentrained bed of solid sulfur oxide acceptor in the gaseous mixture toform a gas depleted of nitrogen oxides; (d) filtering the gas depletedof sulfur oxides and nitrogen oxides and containing entrained loadedsolid sulfur oxide acceptor and particulate matter, to separate a cleangas from filtration solids of loaded solid sulfur oxide acceptor andparticulate matter, the particulate matter generally being present in(d) only if prefiltering is omitted; and (e) passing the clean gas toexhaust in an exhaust gas stream, optionally using an air preheater inthe exhaust gas stream. When the prefiltering step is omitted andparticulate matter is present in the filtration solids, the loaded orspent solid sulfur oxide acceptor is regenerated by (f) classifying bysize the filtration solids of loaded solid sulfur oxide acceptor andparticulate matter into relatively coarse particles of loaded solidsulfur oxide acceptor on a porous carrier material and into relativelyfine particles of particulate matter, e.g., fly ash; (g) regeneratingthe solid sulfur oxide acceptor to form a sulfur dioxide-rich gas andregenerated solid sulfur oxide acceptor; and (h) recycling theregenerated solid sulfur oxide acceptor to form an entrained bed ofsolid sulfur oxide acceptor on a porous carrier in a gaseous mixture.

In one aspect of the process of the present invention the relativelyfine particles of particulate matter from the classifier are carried ina stream of gas and filtered to separate a second clean gas from therelatively fine particles of particulate matter, and the clean gas ispassed to exhaust in an exhaust gas stream. The relatively fineparticles of particulate matter which consist primarily of fly ash, arewaste and are sent to disposal. Optionally, the filtration solids can beheated by air in the classifier, which heated air is used as a stream ofgas to carry the loaded solid sulfur oxide acceptor to the regeneratorand/or the fine particles of particulate matter to a filter after whichthe heated air passes as the stream of exhaust gas through the optionalair preheater and thereafter to the exhaust gas stream.

In another aspect of the present invention, there is provided a systemfor simultaneously removing particulate matter and oxides of sulfur andnitrogen from a gas, such as a combustion exhaust gas stream, by using(a) a reactor capable of forming an entrained bed of sorbent in a gasstream, the sorbent being a solid sulfur oxide acceptor dispersed on aporous carrier material wherein the porous carrier material has anaverage particle size up to about 200 microns when the reactor ispreceded with a particulate matter removal device or an average particlesize of about 20 to about 200 microns when the reactor is not precededwith a particulate matter removal device; (b) optionally, a particulatematter removal device upstream of the reactor to remove particulatematter from the gas stream; (c) means for providing the solid sorbent inthe reactor to form the entrained bed therein; (d) means for injectingammonia gas or a precursor capable of forming ammonia gas into the gasstream; (e) a filter to separate solid sorbent or a mixture of solidsorbent and particulate matter from the gas stream to provide a cleangas stream; (f) optionally, an air preheater in the clean gas stream;and (g) means for passing a gas stream from a gas source, in sequence,to the optional particulate matter removal device, to the reactor, tothe filter, to-the optional air preheater in the clean gas stream andthereafter to the clean gas stream exit.

In accordance with the present invention, there is also provided aregenerative system for simultaneously removing from a gas stream, suchas a combustion exhaust gas stream, particulate matter by means of afilter, oxides of nitrogen by means of ammonia gas and sulfur oxides bymeans of a solid sorbent dispersed on a porous carrier, and forregenerating spent or loaded solid sorbent on a porous carrier, by using(a) a reactor capable of forming an entrained bed of sorbent in a gasstream, the sorbent being a solid sulfur oxide acceptor dispersed on aporous carrier material wherein the porous carrier material has anaverage particle size up to about 200 microns when the reactor ispreceded with a particulate removal device or an average particle sizeof about 20 microns to about 200 microns when the reactor is notpreceded with a particulate removal device; (b) optionally, aparticulate removal device upstream of the reactor to remove particulatematter from the gas stream; (c) means for providing the solid sorbent inthe reactor to form the entrained bed therein; (d) means for injectingammonia gas or a precursor capable of forming ammonia gas in the gasstream; (e) a filter to separate solid sorbent or mixture of solidsorbent and particulate matter from the gas stream to provide a cleangas stream; (f) optionally, an air preheater in the clean gas stream;(g) a clean gas stream exit from the system; (h) means for passing a gasstream from a gas source, in sequence, to the optional particulatematter removal device, to the reactor, to the filter, to the optionalair preheater in the clean gas stream and thereafter to the clean gasstream exit; (i) a classifier optionally required only when a mixture ofsolid sorbent and particulate matter are collected on filter (e), havingmeans to separate the mixture of solid sorbent and particulate matterinto relatively coarse solid sorbent and relatively fine particulatematter collected from filter (e); (j) means for removing the relativelyfine particulate matter carried in a stream of gas from the classifierand means for passing the stream of gas from the classifier to theoptional air preheater in the clean gas stream or to the clean gasstream exit after removal of the relatively fine particulate mattertherefrom; (k) a regenerator for the solid sorbent from filter (e) orclassifier (i), whereby a sulfur oxide-rich gas and regenerated solidsorbent on a porous carrier are formed; (1) means for passing therelatively coarse solid sorbent on a porous carrier from the classifierto the regenerator; and (m) means for passing the regenerated solidsorbent on a porous carrier from the regenerator to the reactor.

As used herein, the terms "sorbent", "acceptor", "solid sulfur oxideacceptor" and "solid sulfur dioxide acceptor" are interchangeable anddefine a solid substance which is capable of binding a gas or a gaseouscompound either physically or chemically, and such sorbents may comprisea porous carrier on which one or more metals and/or metal compounds havebeen deposited, for example, copper and/or copper oxide supported onporous alumina. A loaded or spent sorbent is one which has absorbedand/or reacted with the oxides of sulfur and includes sorbent in whichthe absorption and/or reaction capacity is either totally or partiallyexpended. Loaded or spent sulfur oxide acceptor may include unreactedacceptor or acceptor which still has absorption capacity, mixed with theloaded or spent acceptor, and as used herein, the terms "loaded" or"spent" sulfur oxide include such acceptor material. In accordance withthe present invention, when the sorbent is entrained in a stream of gaswhich contains an oxide of sulfur, such as sulfur dioxide, the sorbentdepletes sulfur dioxide in the gas.

As used herein, the terms "oxides of sulfur", "sulfur oxide" and "sulfurdioxide" mean sulfur dioxide and/or sulfur trioxide and such terms maybe used interchangeably. The terms "nitrogen oxide", "oxides ofnitrogen" and "NO_(x) ", as used herein, mean nitric oxide and/ornitrogen dioxide and may be used interchangeably.

As used herein, the term "particulate matter" or "particulates" refersto the conventional particulate matter emitted from the combustion ofcoal, fuel oil and other fossil fuels and hydrocarbons as well-known inthe art and include emissions from power plants, steel mills, wastetreatment sites, and the like. Particulate matter usually contains ash,for example, fly ash, and/or other material.

As used herein, clean gas is gas which has been treated in the processor system of the present invention and is partially or totally depletedin particulate matter and the oxides of sulfur and nitrogen.

As used herein, entrained bed reactor is a vessel, duct or pipe carryingthe mixture of sorbent entrained in the gas stream.

By the present invention, there is provided an efficient and costeffective regenerative process and system for the simultaneous removalof particulate matter and the oxides of sulfur and nitrogen fromcombustion exhaust gas streams.

Other advantages of the process and system of the present invention willbe apparent from the accompanying drawings and the following detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a diagrammatic representation of the system of thepresent invention.

FIG. 2 is a graph showing sulfur dioxide emission versus time for acopper oxide/alumina sorbent through which sulfur dioxide-containing gaswas passed at three different velocities at a temperature of 700° F.

FIG. 3 is a graph showing sulfur dioxide removal efficiency versus timefor a copper oxide/alumina sorbent used to treat a combustion gas from adiesel engine, the gas containing 210 ppm sulfur dioxide.

DETAILED DESCRIPTION OF THE INVENTION

The process and system of the present invention can be used for thesimultaneous removal of particulate matter and oxides of sulfur andnitrogen contained in a gas stream or mixture of gases. Typical gasstreams containing particulate matter and the oxides of sulfur andnitrogen are well-known in the art, many examples of which are describedin the references cited above.

The solid sorbent used in the process and system of the presentinvention is critical and must be a sorbent which is highly reactive sothat it will require a very short contact time to absorb sulfur dioxideand to reduce nitrogen oxide in the presence of ammonia gas deriveddirectly from ammonia gas or an ammonia gas precursor, examples of whichare well-known in the art.

The solid sorbent must be used in conjunction with a porous support orcarrier material, for example, porous alumina and/or porous silica. Inaccordance with the present invention, the solid sorbent must be coatedon or otherwise associated with the surface or impregnated into the bodyor core, or both, of a porous support or carrier material, for example,a catalytic grade support wherein the porous support or carrier has aparticle size up to about 200 microns, and in certain embodiments aparticle size of about 20 microns to about 200 microns.

Typical sorbents on typical porous carriers are well-known in the artand are described, for example, in U.S. Pat. Nos. 3,501,897; 3,776,854;3,816,597; 3,840,643; 4,001,376; 4,170,627; 4,192,855; 4,258,020;4,609,537; 4,692,318; and U.S. Pat. No. Re. 29,771, all of which areincorporated by reference herein in their entirety. Typical methods ofmaking sorbents on porous carrier materials, typical sorbents, typicaladditives or promoters which act in combination with the sorbent,typical porous carrier materials, typical surface areas and the like aredescribed in the foregoing references.

In preferred embodiments of the present invention, the solid sulfuroxide acceptor or solid sorbent is copper, copper oxide or a mixturethereof coated on and/or impregnated in porous alumina powder,preferably porous activated or gamma alumina. The porosity of thesorbent is generally a function of the porosity of the support orcarrier material, which in turn is a factor in reactivity wherein thesolid sorbent requires only a very short contact time to absorb sulfuroxides and to reduce oxides of nitrogen in the presence of ammonia gascarried in a gas stream in which the solid sorbent on a porous carrier,is entrained. Thus, in accordance with the present invention, thesorbent is highly reactive to 0 promote the use of a reactor capable offorming an entrained bed of sorbent in a gas stream, for example, acombustion exhaust gas stream, such as a flue gas stream from a powerplant.

Porosity of the carrier or support material for the sulfur oxide sorbentof the present invention is critical and must be sufficient so that theresulting sorbent supported or carried thereby has sufficient reactivityto deplete sulfur oxides from a gas stream in an entrained bed reactor.Typically the porous carrier or support material, for example, activatedalumina, has a high surface area of from about 50 m² /gm. to about 500m² /gm. Although porous alumina is the preferred support or carriermaterial, and activated or gamma-alumina are the most preferred supportor carrier materials in accordance with the present invention,, examplesof other refractory inorganic oxides include silica, zirconia, boria,thoria, magnesia, titania, chromia and the like, or composites thereof.Naturally occurring materials, such as, for example porous clays andsilicates such as fuller's earth, attapulgus clay, feldspar, halloysite,montmorillonite, kaolin, and diatomaceous earth, frequently referred toas siliceous earth, diatomaceous silicate, kieselguhr, and the like, andthe naturally occurring material may or may not be activated prior touse by one or more treatments including drying, calcining, steamingand/or acid treatment. As indicated above, the carrier or supportmaterial must be of a porous nature, that is, have a high surface area,to promote high reactivity of the sorbent so that it can be used in anentrained bed reactor, and it must be capable of supporting or carryingthe sulfur oxide acceptor or solid sorbent material.

The porosity of carrier bodies is well-known and described, for example,in U.S. Pat. No. 3,776,854 which is incorporated by reference herein inits entirety. Many carrier bodies are already porous, however porositycan be increased by adding pore-forming agents to the starting materialsprior to forming the material into the desired shape and calcining theshaped material at a temperature, for example, above about 780° C.

The shape of the porous carrier or support material is not critical,however, because of the criticality of the small size of the porouscarrier or support material, that is up to about 200 microns, or incertain embodiments, about 20 microns to about 200 microns, only fineparticles or very small shaped particles (finely-divided particles) canbe used as porous carrier or support material in accordance with thepresent invention.

Typical sulfur oxide acceptors or solid sorbents are described in theabove-cited references, and include, for example, in addition to copper,copper oxide or a mixture thereof, an alkali metal compound, such aspotassium oxide or sodium oxide, promoted with a vanadium compound, suchas vanadium oxide or vanadium pentoxide, or any other metal or metaloxide which is capable of binding sulfur oxides as, for example,sulfate, and which can be regenerated, for example, by means of areducing gas. Naturally, there must be no adverse reaction between thesorbent material and/or the porous carrier or support material, theammonia gas, the ammonia gas precursor, or any other components used inthe process and the system of the present invention.

Although any sorbent on a porous carrier, including any metal or metaloxide on a porous carrier, which is an acceptor for sulfur oxides andwhich is capable of binding or reacting with sulfur oxides, and which iscapable of being regenerated, after it becomes spent, loaded ordeactivated, for example, which may be regenerated by means of areducing gas, or thermal energy, may be used in the process and systemof the present invention, the process and system will be discussedherein with reference specifically to copper-containing sulfur oxideacceptors, for example, copper oxide acceptors, on porous, activatedalumina.

The amount of sorbent on the porous carrier material and/or impregnatedin the porous carrier material is not critical as long as there is asufficient amount of the sorbent, for example, metal or metal oxide, toremove the oxides of sulfur from the gas stream while the sorbent on theporous carrier is entrained in the gas stream and while the sorbent onthe porous substrate is being collected on the filter downstream of thereactor. When the sorbent is copper and/or copper oxide on a porousalumina support, the copper content of the sorbent can, partly dependingon the specific surface area of the material used, vary within widelimits. As a rule it is from about 0.1 to about 15 percent by weightbased on finished sorbent. Optimum results are obtained with sorbentswhich contain from about 4 to about 10 percent by weight of copper. Asindicated above, the porous carrier material is preferably an activatedalumina such as gamma-alumina, an alumina such as alpha-alumina, or amixture of gamma- and alpha-alumina, although in principle all solidsare eligible which are temperature resistant and are not corroded bysulfur oxides and nitrogen oxides under the prevailing conditions.

When copper oxide is the sorbent, the reactions which take place in theprocess and system of the present invention, with SO₂ and NO_(x) in thepresence of ammonia gas are well-known and clearly described in theprior art, for example, flue gas from a combustion source, whichordinarily contains sulfur dioxide, sulfur trioxide, the oxides ofnitrogen, primarily nitric oxide (NO), and particulate matter, as wellas oxygen, react with the copper oxide to absorb SO₂ as shown inequation (1) below.

    2CuO+2SO.sub.2 +O.sub.2 →2CuSO.sub.4                (1)

The copper sulfate formed in equation (1) is regenerated, for example,by a reducing gas such as methane, as shown in equation (2), and thecopper which is formed during the reductive regeneration, is oxidized tocopper oxide by oxygen derived from the flue gas and/or from air addedto the process or system as shown in equation (3).

    2CuSO.sub.4 +CH.sub.4 →2Cu+2SO.sub.2 +CO.sub.2 +2H.sub.2 O (2)

    2CU+O.sub.2 →2CUO                                   (3)

Copper sulfate is also thermally decomposed at temperatures greater thanabout 600° C. as shown in equation (4).

    CuSO.sub.4 --(>600C)→CuO+SO.sub.2 +1/2O.sub.2       (4)

As well-known in the art, the sulfur dioxide produced during theregeneration step as shown in equations (2) and (4) results in a sulfurdioxide rich gas, containing, for example, about 10% to about 40% byvolume sulfur dioxide in air, which in turn can be recovered andconverted by known methods to elemental sulfur and/or sulfuric acid.

The oxides of nitrogen, such as nitric oxide, are reduced by ammonia gasas shown in equation (5) where copper oxide and/or copper sulfate act ascatalyst to the nitric oxide reduction, and nitrogen gas and water areformed from the reduction.

    6NO+4NH.sub.3 --(CuO/CuSO.sub.4)→5N.sub.2 +6H.sub.2 O (5)

Nitrogen gas and water are carried by the clean gas stream to exit thesystem.

Sorbents comprising copper and/or copper oxide preferably supported onporous alumina as a carrier are very suitable for the removal of sulfuroxides from gases under oxidative conditions at temperatures above 500°F., conditions which are normally found in exhaust gases. Under theconditions in which the sulfur dioxide is chemically bound by thesorbent, sulfur trioxide is also removed from the gases.

The amount of ammonia gas or ammonia gas precursor injected into the gasstream is not critical as long as there is a sufficient amount ofammonia gas in the gas stream to reduce and preferably completelydeplete, the NO_(x) content of the gas stream. For the reduction ofnitrogen oxides in the gas stream, ammonia in a quantity of about 0.1 to2.0 times the requisite stoichiometric quantity is supplied to the gasto be treated. In preferred embodiments, the ammonia gas used in the gasstream is from about a 0.1:1 to about a 1.1:1 mole ratio with thenitrogen oxides content of the gaseous mixture.

According to the process and system of the invention, substantialquantitative reduction of NO_(x) can be achieved. Ammonia is generallynot detected in the flue gases treated. Instead of gaseous ammonia it isalso possible to add precursors of ammonia, such as an aqueous solutionof ammonia, or a ammonium carbonate solution, urea, hydrazine, ethylenediamine or hexamethylene diamine.

For the process and system of the present invention to be economical, itis necessary that the sorbent on a porous carrier be capable ofregeneration a substantial number of times without loss of activity andstability, for example, a sorbent should be capable of regeneration manytimes with only 1 percent (by weight) or less addition of fresh sorbenton a porous carrier to make-up for losses and/or reduced activity.

The regenerator may be any conventional type of reactor, including fixedbed, moving bed, fluidized bed and the like. In accordance with thepresent invention, the fluidized bed type of regenerator is preferredwherein the hot regenerating gas or gases or hot air and the like areinjected into a fluidized bed. The regeneration under reducingconditions typically takes place at a temperature as low as about 600°F. to about 1200° F., however, in certain preferred embodiments, theregeneration may take place in heated air at temperatures over about1200° F., and more preferably,, about 200° F. to about 1800° F.

The regeneration of sorbents of the present invention, may be achievedby any of the systems and processes known in the art. Conventionalreducing gases, such as methane, ethane, propane and the like, may beused, or a reducing gas, such as hydrogen, carbon monoxide or ahydrogen-containing gas diluted with steam, may be used.Hydrocarbon-containing gases, such as the off-gas from a catalyticreformer, are also suitable for the regeneration of sulfur oxide loadedmetal-containing catalysts. Suitable hydrogen- and CO- containing gasesmay be obtained by partial oxidation or steam-reforming of hydrocarbonsand from coal gasifiers.

The gas stream or mixture of gases which may be treated in the processand system of the present invention may be derived from any suitablesource, such as exhaust gases, and more specifically, from a combustionexhaust gas stream, which contains particulate matter, oxides ofnitrogen and sulfur oxides.

Although the compositions of gas streams and mixtures of gases varywidely, depending on the particular source of the gas stream, typicallysuch exhaust gases contain between 500 and 10,000 ppmv SO₂ and betweenabout 100 and 2,000 ppmv nitrogen oxide, calculated as NO. In additionto SO₂ and nitrogen oxides, the exhaust gases contain nitrogen, watervapor and CO₂ as well as residual oxygen.

As shown in FIG. 1, an exhaust gas source is derived, for example, fromboiler 2 which is fed by a stream of coal 12 and air 14. A stream ofcombustion exhaust gas containing particulate matter, such as fly ashand the oxides of sulfur and nitrogen, flows in duct 16 at a temperatureof about 600° F. to about 900° F. into a particulate removal device 4,for example, a cyclone, to remove coarse fly ash from the exhaust gasstream in duct 16. The fly ash collected from the gas stream inmechanical particulate removal device 4 is removed therefrom by asuitable outlet 62, and fly ash and other particulate matter collectedin particulate removal device 4 is discharged as appropriate, forexample, to waste.

Generally, the average particle size of particulate matter, such as flyash, derived from the combustion of coal, hydrocarbon fuel and the like,has an average particle size of less than 20 microns, defined herein asrelatively fine particles of particulate matter. When the particulatematter in the combustion exhaust gas stream in duct 16 has a particlesize less than about 20 microns, then particulate removal device(cyclone) 4 is optional and can be by-passed, or alternatively, can beomitted from the system. Thus, it is only when the particulate matter inthe combustion exhaust gas stream has a particle size of about 20microns or greater, that is, when the particulate matter in thecombustion exhaust gas stream is coarser than or about the same size asthe sorbent, that is, solid sulfur oxide acceptor on a porous carrier,that particulate matter must be removed from the exhaust gas stream inparticulate removal device 4, otherwise designated herein as aprefiltering device 4.

As indicated above, prefiltering device 4 is only necessary when theparticulate matter, such as fly ash, in the combustion exhaust gasstream fed to the system is of a particle size which is substantiallythe same as or coarser than the sorbent used to remove the oxides ofsulfur from the combustion exhaust gas stream. If the particulate matterin the combustion exhaust gas stream is less than about 20 microns, itcan be separated from a sorbent, having a particle size of about 20microns to about 200 microns, in a classifier located downstream of theentrained bed reactor and a particulate matter filter, wherein theclassifier separates the mixture of solid sorbent having a particle sizeof about 20 microns to about 200 microns and particulate matter having aparticle size of less than 20 microns into relatively coarse solidsorbent which would include relatively coarse particulate matter, suchas fly ash, if present, and into relatively fine particulate matter,which is primarily particulate matter, such as fly ash,, having aparticle size less than 20 microns.

From the foregoing, it is also clear that if particulate matter in thecombustion exhaust gas stream is removed by the optional particulateremoval device or prefiltering device 4, the particle size of thefinely-divided sorbent can also include particle sizes less than 20microns, and thus include particles having a size up to about 200microns when the particulate matter is removed from the combustionexhaust gas stream flowing through duct 16. The combustion exhaust gasstream prefiltered in prefiltering device 4 passes by any suitable meansfrom prefiltering device 4 to reactor 6, or alternatively, if there isno prefiltering device 4, or if prefiltering device 4 is by-passed,directly from duct 16 to reactor 6.

Reactor 6 is any suitable device wherein a solid material can beentrained in a gas stream flowing through the device. In its simplestform in accordance with the present invention, reactor 6 is merely aduct identical to or similar to ducts 16 and/or 18. It can also be aconduit, a vessel and the like, including any other device or apparatuswherein solids can be injected or passed into a stream of gas passingtherethrough and wherein the solids become entrained in the gas stream.The formation of the entrained bed is dependent upon the velocity of thegas stream, for example, a combustion exhaust gas stream, flowingthrough reactor 6. A simple injector port, pipe or vent 70 can be usedto inject solids into the combustion exhaust gas stream in reactor 6 sothat they will become entrained therein.

In reactor 6, an entrained bed of sorbent wherein the sorbent is a solidsulfur oxide acceptor dispersed on a finely-divided porous carriermaterial and wherein the finely-divided porous carrier material has anaverage particle size up to about 200 microns when the reactor ispreceded with particulate removal device 4 and an average particle sizeof about 20 microns to about 200 microns when the reactor is notpreceded with particulate removal device 4, is formed as explainedabove. Fresh or make-up sorbent is added to reactor 6 at inlet 72 and 70where the solid sorbent becomes entrained in the gas stream enteringreactor 6 through duct 18, and as explained above.

The gas stream entering reactor 6 must have a velocity which willentrain the solid sorbent injected 35 therein, and accordingly, thevelocity of the gas may be any velocity sufficient to form an entrainedbed of solid sorbent therein and propel the solid sorbent to a suitablefiltering device. The velocity of combustion exhaust gas streams frompower plants, diesel engines and other common sources is generallysufficient to form the entrained bed of sorbent in the combustionexhaust gas stream without further assistance.

When the regenerative system is in operation, solid sorbent injectedinto reactor 6 is primarily derived from regenerated solid sorbent froma regenerator through a suitable conduit 50. This is discussed in moredetail below.

Ammonia gas or a precursor capable of forming ammonia gas is alsoinjected into the exhaust gas stream. In FIG. 1, ammonia gas injector 20provides ammonia gas in the combustion exhaust gas stream in reactor 6where the ammonia gas is also entrained in the combustion exhaust gasstream. In alternative embodiments (not shown) ammonia gas or aprecursor capable of forming ammonia gas can be injected into thecombustion exhaust gas stream prior to reactor 6, for example, in duct18 or subsequent to reactor 6, for example, in duct 22. In accordancewith the present invention, the particular part of the system in whichthe ammonia gas or precursor is injected therein, is not critical andcan be easily chosen by one skilled in the art.

As the sorbent and ammonia gas become entrained in the combustionexhaust gas stream and travel therewith through reactor 6 and thereafterthrough duct 22, the ammonia reacts with the NO_(x) to produce elementalnitrogen and water, and the sulfur oxides react with and/or are absorbedon the sorbent. When the sorbent is copper oxide, the reaction shownabove takes place and copper sulfate is formed in the gas stream.

The entrained bed passes through duct 22 into filter 8 where the solidsorbent having reacted and absorbed oxides of sulfur thereon or amixture of solid sorbent having oxides of sulfur reacted and absorbedthereon and particulate matter, if present, are separated from thecombustion exhaust gas stream to form a clean gas which exits filter 8by means of a suitable duct 24. In preferred embodiments, filter 8 is ahigh temperature filter suitable forefiltering the hot gas, for example,a ceramic or fiber metal filter. In filter 8, any solids which arefiltered from the gas stream, also form a filter cake of sorbent whichgenerally contains partially depleted or in certain cases, amounts offiltered reactive sorbent, and the removal of the oxides of sulfur andnitrogen continues in the filter cake in filter 8, thereby assisting inthe removal of the oxides of sulfur and nitrogen from the gas stream. Incertain embodiments, the entrained bed reactor residence time may bevery short and most of the removal of SO₂ and NO_(x) will occur in thefilter cake in filter 8.

Clean gas leaving filter 8 in duct 24 proceeds to a clean gas streamexit 26 from the system, for example, an exhaust gas stack. In certainembodiments, an optional air preheater 10 may be placed in the clean gasstream so that clean gas from duct 24 passes through the air preheater10 before it flows to clean gas stream exit 26. Air preheater 10 may beany conventional heat exchanger which extracts heat from clean gaspassing therethrough. Air preheater 10 extracts heat from the combustionexhaust gas stream and provides heat for the air that goes to theboiler, for example, air preheater 10 heats the air provided in stream14.

Filter 8 removes only spent sorbent when prefiltering device 4 is usedto remove all particulate matter from the combustion exhaust gas stream.If prefiltering device 4, for example a cyclone, removes only relativelycoarse particles of particulate matter from the combustion exhaust gasstream, then relatively fine particulate matter may be entrained in thecombustion exhaust gas stream in duct 18 which enters reactor 6 and isfiltered by filter 8. Further, if prefiltering device 4 is omitted fromthe system, or if it is bypassed, then filter 8 removes spent sorbentand particulate matter from the combustion exhaust gas stream where itis collected as filtration solids and may be removed by means of hoppersin conduits 28 and 32.

If a mixture of spent sorbent and particulate matter are collected byfilter 8, then the mixture passes through conduits 28 and 32 toclassifier 30 where the mixture is separated into relatively coarse butfinely-divided solid sorbent and relatively fine particulate matter. Asused herein, the solid sorbent is considered finely-divided even thoughit is the relatively coarse fraction separated from classifier 30.

Classifiers are well-known and well-defined in the art for classifyingparticles by size from a flue gas stream to produce a quantity ofrelatively coarse particles and a quantity of relatively fine particles.An example of classification is found in U.S. Pat. No. 4,193,972 whichis incorporated by reference herein in its entirety. Generally, in theclassifier in accordance with the present invention, the relativelycoarse particles are those having an average particle size of about 20microns and larger and relatively fine particles are those having aparticle size of less than about 20 microns. Any device well-known inthe art which is capable of separating relatively coarse particles fromrelatively fine particles may be used to classify and separate therelatively coarse particles of finely-divided spent sorbent from therelatively fine particles of particulate matter in accordance with thepresent invention.

The classifier can also serve as a sorbent heater by using a stream ofhot air 42 as a carrier gas to conduct the classified solids, that is,the relatively coarse finely-divided spent sorbent and/or the relativelyfine particulate matter in transporting the foregoing from classifier30. The relatively fine particulate matter is primarily particles of flyash and is removed from classifier 30 by stream 34 (suitable duct) tofilter 36 where the particulate matter can be separated from the carriergas stream, and-the carrier gas stream can be discharged to exhaust byconduit 38 which can be fed to the air preheater 10 in clean gas stream24 and thereafter to clean gas stream 26. The particulate matterfiltered by filter 36, for example, a baghouse, can be removed throughconduit 48 and discharged to waste.

The finely-divided spent or loaded sorbent from classifier 30 or thefinely-divided spent or loaded sorbent from filter 8 when particulatematter has been prefiltered by particulate removal device orprefiltering device 4, passes by suitable conduit 46 to regenerator 40.Thus, when only spent sorbent is present in filter 8, spent sorbentremoved by means of suitable conduits 28 and 32 can flow directly intoregenerator 40 and bypass classifier 30, or classifier 30 can be omittedfrom the system.

The spent or loaded sorbent in regenerator 40 is regenerated to form agas which is rich in sulfur oxides. The gas which is rich in sulfuroxides, for example, a sulfur dioxide-rich gas passes by suitableconduit 52 to sulfur oxide recovery unit 60 where sulfur oxides, forexample, sulfur dioxide can be converted into elemental sulfur and/orsulfuric acid which passes from sulfur oxide recovery unit 60 viasuitable conduit 58 for recovery. Generally, in accordance with thepresent invention, the sulfur dioxide rich gas which passes throughconduit 52 from regenerator 40 to sulfur oxide recovery unit 60 has asulfur dioxide content of about 10 percent to about 40 percent byvolume.

The finely-divided spent or loaded sorbent, for example spent or loadedcopper oxide/copper sulfate-coated porous alumina powder generally has asmall copper oxide to copper sulfate ratio due to the reactivity of thesorbent. The spent sorbent is regenerated in regenerator 40 by anyconventional method, for example, by using a reducing gas, such asnatural gas, methane, ethane, propane and the like as well-known in theprior art and which is shown as entering regenerator 40 by means ofstream 54 or by thermal decomposition using hot air at a temperaturegreater than about 1200° F. and preferably at a temperature of about1200° F. to about 1800° F. The regenerated sorbent is reinjected intoreactor 6 through stream 50 where it becomes entrained in the combustionexhaust gas stream from duct 18.

The foregoing system may be easily adapted for the simultaneous controlof the oxides of sulfur, the oxides of nitrogen and particulate matterfound in the combustion gases of power plants, diesel engines andindustrial boilers and the like.

The following specific examples describe the process and system of thepresent invention. They are intended for illustrative purposes only andshould not be construed as limiting the present invention.

A typical sorbent was made by soaking activated alumina powder having anaverage particle size of about 20 to about 100 microns in diameter, in awater-soluble copper salt such as copper nitrate or copper sulfate. Thesoaking is following by drying and calcining of the powder. Theimpregnated powder is highly reactive.

In laboratory fixed bed tests a greater than 99 percent removalefficiency was consistently achieved using a 1 mm to 5 mm thick cake ofpowder which was allowed to settle on a high temperature fiber metalfilter element, containing about 5.2 percent by weight copper. The inletconcentration of sulfur dioxide was 310 ppmv with temperatures in therange of about 500° F. to about 800° F. and a gas velocity in the rangeof 4.3 ft. per minute to about 15 ft. per minute. Typical test resultsfor the foregoing tests on the filter cake are shown in FIG. 2 where thegas velocity was 4.3 ft. per minute, 7.5 ft. per minute and 10 ft. perminute and the cake thickness was 1 mm.

The fixed bed test shown in FIG. 2 illustrates that the existence ofcopper oxide on a finely-divided (small in diameter), porous aluminapowder increases the reactivity and utilization of the copper oxide andthat only a short contact time is needed for reaction to occur betweenthe copper oxide-coated powder and ammonia gas injected into the mixtureof oxides of sulfur and oxides of nitrogen in a gas stream.

The process of the present invention takes advantage of a short contacttime by using the finely-divided copper oxide-coated porous aluminapowder in a relatively high velocity gas stream containing the oxides ofsulfur, oxides of nitrogen and particulate matter typical of theeffluent gases from power plants, diesel motors and the like. The use ofan entrained bed of copper oxide-coated, finely-divided porous aluminapowder in average particle sizes up to 200 microns, and in certainembodiments from about 20 microns to about 200 microns, in an entrainedbed reactor, for example, in a flue gas duct, eliminates the use oflarge reactor vessels that are conventionally used for the simultaneousremoval of oxides of sulfur, oxides of nitrogen and particulate matter.

In another experimental system built to remove oxides of sulfur, oxidesof nitrogen and particulate matter from the exhaust gas of a dieselengine, the system included injector means to inject copper oxidecoated, finely-divided porous alumina particles having an averageparticle size of about 20 to about 100 microns in diameter, into theexhaust pipe of the diesel engine, as well as an injector to injectammonia gas into the exhaust pipe. A filter was located downstream ofthe exhaust pipe to capture particulate matter in the combustion gas aswell as the injected finely-divided copper oxide coated aluminaparticles. Collected particles on the filter downstream of the exhaustpipe were removed from the filter elements by a reverse pulse jet aswell-known in the art. The reverse pulse jets were staggered so thatabout 1/3 of the filter media downstream of the exhaust pipe was cleanedwith each pulse. The filter media was made of fiber metal and was builtto operate at temperatures up to about 1000° F. The filter elements inthe filter were candle filters with a total of 7.5 sq. ft. of filtermedium. Combustion gas velocity through the filter medium was 8.0ft./min. Conventional detectors were used to measure the inletconcentration of sulfur dioxide and of nitrogen and the outletconcentration of sulfur dioxide and oxides of nitrogen.

The foregoing system operated at the diesel engine exhaust gastemperature of about 700° to about 800° F. and a gas flow rate of 60acfm (air-to-cloth ratio of 8 ft./min).

FIG. 3 shows the sulfur dioxide removal efficiency as a function ofengine running time. The exhaust gas from the diesel engine containedabout 210 ppmv sulfur dioxide prior to treatment and after the dieselengine had been running for about 40 minutes, sorbent injection into theexhaust gas stream was initiated. The increased sulfur dioxide removalefficiency with time, as illustrated in FIG. 3, was due to an increasein the rate of sorbent injection and to the accumulation of sorbent onthe filter elements. Removal efficiency of 95 percent was achieved atabout 90 minutes into the run. At about 90 minutes into the run, filtercake was removed from 1/3 of the elements by reversed air pulse jetwhich resulted in a short duration drop in sulfur dioxide removalefficiency to 70 percent. Efficiency increased in a short duration toabout 90 percent to 95 percent after the cleaning. Cleaning cycles, thatis, cleaning of the filter cake from 1/3 of the filter elements byreverse air pulse jet, were activated at 120 minutes and 145 minutesinto the run resulting in short duration efficiency drops to 75 percentand 85 percent respectively as shown in FIG. 3.

Simultaneously with the injection of finely-divided copper oxide-coatedporous alumina particles into the exhaust gas of the diesel engine,ammonia gas was injected into the exhaust gas duct. The inletconcentration of the oxides of nitrogen, that is the concentration ofthe oxides of nitrogen prior to treatment with ammonia gas, was about600 ppmv. At an ammonia gas/nitrogen oxide ratio of 0.91, a nitrogenoxide (NO_(x)) reduction of up to 87 percent was observed. In view ofthe fact that 10 percent of the NO_(x) is at an oxidation state higherthan NO, the Ammonia slip is believed to be negligible.

The foregoing test shows that a removal efficiency of sulfur dioxidegreater than 95 percent can be achieved in a system and process using anentrained bed of finely-divided copper oxide-coated porous aluminaparticles having a particle size of about 20 to about 100 microns usedin conjunction with a filter. Higher removal efficiency can be achievedwith an increase in CuO to SO₂ ratio by increasing the sorbent injectionrate and/or by increasing the sorbent residence time in the entrainedbed reactor.

While other modifications of the invention and variations thereof whichmay be employed within the scope of the invention, have not beendescribed, the invention is intended to include such modifications asmay be embraced within the following claims.

What is claimed is:
 1. A regenerative system for simultaneously removingtime a combustion exhaust gas stream, particulate matter by means of afilter, oxides of nitrogen by means of ammonia gas and sulfur oxides bymeans of a solid sorbent on a porous carrier, and for regenerating spentsolid absorbent on a porous carrier, comprising:(a) an entrained bedsolid sorbent reactor in a combustion exhaust gas stream; (b) means forproviding a solid sulfur oxide acceptor sorbent in the reactor to forman entrained bed therein, said solid sulfur oxide acceptor sorbent beingdispersed on a finely-divided porous carrier material wherein thecarrier material has an average particle size up to about 200 micronswhen said reactor is preceded with a particulate removal device and anaverage particle size of 20 microns to 200 microns when the reactor isnot preceded with a particulate removal device; (c) means for injectingammonia gas or a precursor of ammonia gas into the exhaust gas stream;(d) a filter to separate solid sorbent, particulate matter, or a mixtureof solid sorbent and particulate matter from the exhaust stream toprovide a clean gas stream; (e) a clean gas stream exit from the system;(f) means for passing the combustion exhaust gas stream from acombustion exhaust gas source, in sequence, to the reactor, to thefilter and thereafter to the clean gas stream exit; (g) a regeneratorfor regenerating the solid sorbent dispersed on a porous carriermaterial and containing no particulate matter from filter (d) whereby asulfur oxide-rich gas and regenerated solid sorbent are formed; (h)means for passing the solid sorbent dispersed on a porous carriermaterial from the filter to the regenerator; and (i) means for passingthe regenerated solid sorbent dispersed on a porous carrier materialfrom the regenerator directly to the reactor.
 2. A system according toclaim 1 wherein said entrained bed solid sorbent reactor is a duct inthe combustion exhaust gas stream, said duct having said means forproviding a solid sulfur oxide acceptor sorbent therein, and anentrained bed of sorbent forms therein when sorbent is introduced intothe combustion exhaust gas stream passing through the duct.
 3. A systemaccording to claim 1 wherein the filter to separate solid sorbent or amixture of solid sorbent and particulate matter from the exhaust gasstream is a filter which withstands a gas temperature up to 1000° F. 4.A system according to claim 1 wherein the means for passing thecombustion exhaust gas stream from the combustion exhaust gas source areflue gas ducts sequentially connected from the combustion exhaust gassource to the reactor, from the reactor to the filter, and from thefilter to the clean gas stream exit.
 5. A system according to claim 1wherein said means for providing a solid sulfur oxide acceptor sorbentin the reactor is a solids injector and the solid sulfur oxide acceptorsorbent is copper, oxide, regenerated copper, regenerated copper oxideor mixtures thereof on a porous alumina carrier.
 6. A system accordingto claim 1, further comprising a classifier having means to separate aloaded solid sulfur oxide acceptor sorbent from particulate mattercollected as the mixture of solid sorbent and particulate matter onfilter (d).
 7. A system according to claim 1 wherein the regenerator isa hot, reducing gas-fed regenerator.
 8. A system according to claim 1wherein the regenerator is a heated air thermal regenerator constructedand arranged to be heated at a temperature of about 1200° F. to about1800° F.
 9. A system according to claim 1, further comprising aparticulate removal device upstream of said reactor to removeparticulate matter from the combustion exhaust gas stream and the porouscarrier material having solid sulfur oxide acceptor sorbent dispersedthereon in said reactor, has an average particle size up to about 200microns.
 10. A system according to claim 9 wherein the particulateremoval device upstream of the reactor is a cyclone separator.
 11. Asystem according to claim 1, further comprising an air preheater in theclean gas stream.
 12. A system according to claim 1, further comprisinga classifier having means to separate the mixture of solid sorbentdispersed on a porous carrier material and particulate matter collectedon filter (d);means for removing the particulate matter carried in astream of gas from the classifier and means for passing the stream ofgas from the classifier to the clean gas stream exit after removal ofthe particulate matter therefrom; and means for passing the solidsorbent dispersed on a porous carrier material from the classifierdirectly to the regenerator.
 13. A system according to claim 12 whereinthe means for removing the particulate matter carried in a stream of gasfrom the classifier is a filter.